X-ray crystal structures of 1,2,4-tri-O-acetyl-5-deoxy-3-O-methyl-5-[(S)-phenylphosphinyl]-α-d-xylopyranose and its 5-[(S-phenylphosphinothioyl] derivative, and conformations of d-xylopyranose analogs having a C₆H₅P(R) group in the hemiacetal ring

X-ray crystallographic analyses are reported for the two title compounds (8 and 9, of which the former crystallized in two modifications (8a and 8b). In all three structures, the pyranose rings have the ⁴C₁ (d) conformation and the substituents at C-1 are axial and those at C-2-C-4 are equatorial. The phenyl rings are oriented equatorially with their planes nearly parallel to the axial P R bond (R O, S). The favored conformations of various PhP( R)-in-ring d-xylopyranose acetates (R O,S, lone-pair; 8-19) in solution are discussed. The inclination of the equatorial P-phenyl group of the α- and β-d-xylopyranose analogs 8-13 is similar to that observed in the solid, whereas the inclination of the axial phenyl ring of the P-5 epimers 14-19 is near 90° with respect to the equatorial P R bond.